Field of the Invention
The present invention relates to a circuit board including a plurality of terminals for connection to electric components and a liquid ejection head including the circuit board.
Description of the Related Art
As a circuit board of this kind, Japanese Patent Laid-Open No. 2003-72042 describes a flexible circuit board connected to a printing element substrate in an ink jet print head (liquid ejection head). The circuit board is bonded on a support substrate that supports the printing element substrate and assembled to the print head along with the printing element substrate and the support substrate. Such a circuit board is provided with a plurality of inner terminals connected to respective plurality of electrodes on the printing element substrate, a plurality of outer terminals connected to a circuit in a main body of a printing apparatus, and wire patterns that connect the inner terminals and the corresponding outer terminals together.
The circuit board is bonded, with an adhesive, to the support substrate via an insulation layer positioned on the wire pattern. A surface of the insulation layer slightly undulates according to the shape of the wire patterns, and the adhesive bonds the undulating surface of the insulation layer to a surface of the support substrate. Thus, when the circuit board is bonded to the support substrate, a space between the circuit board and the support substrate that holds the adhesive is narrower at portions of the adhesive applied to areas where the wire pattern is present than at portions of the adhesive applied to areas where the wire pattern is not present. As a result, each of the former portions of the adhesive tends to be spread out to the corresponding areas where the wire pattern is not present. Furthermore, in these bonding areas, flow resistance of the adhesive may vary according to the undulating shape of the insulation layer, leading to uneven spread of the adhesive. Consequently, in the bonding area where the adhesive is likely to spread, the adhesive may leak to the exterior, whereas, in the bonding area where the adhesive is unlikely to spread, inappropriate bonding may occur. In Japanese Patent Laid-Open No. 2003-72042, such uneven spread of the adhesive is not taken into account.